WHAT ARE POINT, AREA, AND MOBILE SOURCES?

Air toxics are emitted from many types of sources. These sources of air pollution are generally categorized as point, area, and mobile sources. For the 1999 NATA, USEPA defines them in the following way:

Major Point Sources: A point source is a stationary facility or process that emits a significant amount of air pollution during manufacturing, power generation, heating, incineration, or other such activity. For NATA, USEPA called this category "Major Sources," and included in it just those sources which emit at least 10 tons per year of any one hazardous air pollutant (HAP), or at least 25 tons per year total of any HAPs. Major point sources include power plants; refineries; municipal waste incinerators; toxic waste transfer, storage and disposal facilities (TSDFs); TRI sources (facilities that are required to report their emissions under the Toxic Release Inventory program); and other sources that must report emissions under other state and federal programs.

Area and Other Sources: These are small sources of air pollution which by themselves may not emit very much but, when their emissions are added together, account for a significant portion of the total emissions of air toxics. In NATA, USEPA refers to this category as "Area and Other Sources," and includes small industrial sources that fall below the "major source" threshold. Area sources are often too small or too numerous to be inventoried individually. The following are grouped under area sources in NATA:

BACKGROUND CONTRIBUTION
Some of the 177 air toxics evaluated in NATA are no longer emitted in significant quantities, but levels in air persist from past emissions. For a discussion of background concentrations, click here.

THE 1999 EMISSION INVENTORY
As part of the National-Scale Air Toxics Assessment (NATA), USEPA prepared a comprehensive list of air toxics emissions for the entire country in 1999. The emissions inventory for New Jersey was briefly reviewed and revised by NJDEP before being finalized by USEPA. Although there are bound to be some errors in the details of a massive undertaking such as this, a summary of the emissions inventory can give us some indication of which may be the most important sources of air toxic emissions in our state. As can be seen from the pie chart below, mobile sources are the largest contributors to air toxics emissions in New Jersey, with on-road mobile sources accounting for 36%, and non-road mobile sources contributing 25%. Area sources represent 27% of the inventory. (USEPA refers to this category as "Area and Other" because it includes residential, commercial, and small industrial sources.) The remaining 12% of the inventory is attributable to major industrial sources. Major sources are defined by the Clean Air Act as facilities that emit more than 10 tons per year of a single hazardous air pollutant (HAP) or 25 tons per year of all HAPs combined.

USEPA also compiled an air toxics emissions inventory for the 1996 NATA, which was released in 2002, and for the 1990 Cumulative Exposure Project (CEP). The 1996 NATA and 1990 CEP results were discussed on this website previously, and can still be accessed by clicking here. However, USEPA emphasizes that the methods used to conduct the 1990, 1996 and 1999 emissions inventories are different, so that the results for the three different years cannot be compared directly.

COMPARISON OF EMISSIONS BY COUNTY
When the New Jersey emissions estimates are broken down by county, it is evident that the areas with the largest air toxic emissions are generally those with the largest population in the smallest space. This is directly related to high levels of vehicle use, solvent use, and other population-related types of activities in those counties.

COMPARISON OF EMISSIONS BY SQUARE MILE
The chart below shows New Jersey’s emissions in tons per year per square mile, which is primarily related to population density. Hudson County is the smallest county by area, but by far the most densely populated (13044 people per square mile, compared to the statewide average of 1134 people per square mile – 2000 U.S. Census data).